Sweden's domestic intelligence agency said it would probe why the government's website crashed on Sunday amid reports hackers had sought revenge for a crackdown on alleged online piracy.
The government website went off line in the early hours of Sunday. The Internet home page of the national police crashed in similar fashion on Thursday.
The police website problem came a day after the Pirate Bay Internet page, which the recording industry calls a major source for downloading pirated music and films, was shut by police.
"They (the government) contacted us and wanted to make a police complaint that something has happened with their home page and it is now a question for us investigate if it is a crime or something else," said Anders Thornberg, a spokesman for the Security Police intelligence agency.
Local media said hackers attacked both sites, now functioning again, after the clampdown on Pirate Bay. Pirate Bay is also up and running again.
Sweden's Emergency Management Agency earlier warned all 31 bodies involved in emergency management, such as the police and rescue services, and all 21 local authorities to ensure they were safe from attacks on their websites.
Newspaper Aftonbladet quoted a group called World Wide Hackers as saying they had arranged an attack on the government's website.
Sweden last year banned the downloading of copyright protected music and movies from the Internet after being singled out for criticism by Hollywood. The raid on Pirate Bay was the latest of several actions against suspected online piracy.
Critics say the police are heavy handed and that people should have access to free information via the Internet, including file sharing.
Several hundred people demonstrated in Stockholm on Saturday in support of Pirate Bay.
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